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Nd : Bi4Ge3O12 Crystal Growth by Czochralski Method
Bae, In Kook,Whang, Chin Myung 대한금속재료학회(대한금속학회) 1999 METALS AND MATERIALS International Vol.5 No.5
Nd-doped Bi₄Ge₃O_(12) (Nd:BGO) crystals were successfully grown in the auto-diameter control system equipped with a frequency weighing sensor with the Czochralski method. The Nd^(3+) ion doping level was varied from 0.25 to 2.5 at.%. The crystals were transparent and of light purple color, with a typical size of about 20 mm in diameter and 50 mm in length. The effective distribution coefficient (K_(eff)) of Nd^(3+) ion was about 0.957 irrespective of concentration, and the Nd^(3+) ions were distributed homogeneously throughout the crystal. The doping concentration (ρ_i) of active ion in Nd:BGO crystal was 2.54×10^(20) ions/㎤, which is higher than that in the Nd:YAG crystal. Therefore, the Nd:BGO crystal was judged to be more suitable for the laser diode pumping microchip laser material where size reduction was desirable.
Oh, Eun‐,Ok,Whang, Chin‐,Myung,Lee, Yu‐,Ri,Park, Sun‐,Young,Prasad, Dasari Hari,Yoon, Kyung Joong,Son, Ji‐,Won,Lee, Jong‐,Ho,Lee, Hae‐,Weon WILEY‐VCH Verlag 2012 Advanced Materials Vol.24 No.25
<P><B>An extremely thin bilayer electrolyte</B> consisting of yttria‐stabilized zirconia (YSZ) and gadolinia‐doped ceria (GDC) is successfully fabricated on a sintered NiO‐YSZ substrate (see figure). Major processing flaws are effectively eliminated by applying local constraints to YSZ nanoparticles, and excellent open circuit voltage and cell performance are demonstrated in a solid oxide fuel cell (SOFC) at intermediate operating temperatures.</P>
Gupta, Ravindra K,Whang, Chin Myung IOP Pub 2007 Journal of physics, an Institute of Physics journa Vol.19 No.19
<P>The effect of composition on the structure of the new solid oxide fuel cell (SOFC) perovskite (La<SUB>1−<I>x</I></SUB>Sr<SUB><I>x</I></SUB>)(Cr<SUB>0.85</SUB>Fe<SUB>0.05</SUB>Co<SUB>0.05</SUB>Ni<SUB>0.05</SUB>)O<SUB>3−δ</SUB> is studied using x-ray diffractometry, pycnometry, and Fourier-transform infrared and Raman spectroscopy. Samples were synthesized using the Pechini method via doping the La site with Sr<SUP>2+</SUP>, to a composition with <I>x</I> = 0–0.4 mole fraction, and at the Cr site with 0.05 mol of Co<SUP>2+</SUP>,Fe<SUP>2+</SUP> and Ni<SUP>2+</SUP>, and the structural results were compared with those for orthorhombic LaCrO<SUB>3</SUB>. The samples were orthorhombic perovskite of the <I>Pnma</I> space group. A second phase, monoclinic SrCrO<SUB>4</SUB>, was also observed, whose content increased linearly with increasing <I>x</I>. A large decrease in the lattice and hence volume was observed for the sample with <I>x</I> = 0.1, which was accompanied by a sharp decrease in the Cr−O bond length, tilt angle and crystallite size. The structural parameters were almost invariant for <I>x</I> = 0.1–0.4, probably due to an increase in content of the high valence cations of smaller ionic radii, as suggested by an increase in the intensity of the defect band (∼515?cm<SUP>−1</SUP>, IR). The octahedral CrO<SUB>6</SUB> stretching, bending and tilting modes were found shifted accordingly. A mechanism employing a partial-charge model was proposed to explain the results. </P>
Eun, Hee-Tai,Whang, Chin-Myung The Korean Ceramic Society 1996 The Korean journal of ceramics Vol.2 No.2
The Mg-PSZ/$Al_2O_3$ fibers were fabricated by the sol-gel method. The added $Al_2O_3$ amounts were varied from 5 to 20 mol%. The phase transformation studies of a drawn Mg-PSZ/$Al_2O_3$ fibers were investigated by use of X-ray diffraction, IR and Raman spectroscopy. Microstructure and tensile strength of fibers were subjected to scanning electron microscopy and tensile strength tester. When $Al_2O_3$ was added to the Mg-PSZ fibers, it was found out from the analysis of XRD patterns and Raman spectra that a small amount of crystalline spinel($MgAl_2O_4$) started to form due to the reaction between $Al_2O_3$ and MgO, at $1000^{\circ}C$, and the phase transformation temperature of $ZrO_2$ crystal phase at different sintering temperatures increased. Also, the rapid grain growth with average size of 2.0 ${\mu}m$ shown in Mg-PSZ fiber at $1500^{\circ}C$ was considerably suppressed to 0.39 ${\mu}m$ by adding $Al_2O_3$ at the same temperature. When the Mg-PSZ/$Al_2O_3$ fibers containing 5 mol% $Al_2O_3$ were sintered $800^{\circ}C$ for 1 hr, average tensile strength of fibers was 0.9 GPs at diameters of 20 to 30 ${\mu}m$, but as the sintering temperatures was increased to $1000^{\circ}C$ for 1 hr, average tensile strength of fibers increased to 1.2 GPa in the same diameter range.
FT-IR 및 Raman 분광법에 의한 $Na_2O$-$Ga_2O_3$-$SiO_2$ 계 유리의 구조분석
황진명,이전,배인국,Whang, Chin-Myung,Rhee, Jhun,Bae, In-Kook 한국세라믹학회 1988 한국세라믹학회지 Vol.25 No.1
In order to investigate the reason of changes in the physical properties of glasses near the region for which R(Ga/Na)=1, spectroscopic studies using FT-IR and Raman spectroscopy have been carried out on Na2O.2SiO2 glass with addition of Ga2O3 from 0 to 35 mole %, i.e., from R=0 to 1.61. The main purpose of this work is to investigate the coordination number of Ga3+ in glass with variation of glass composition and to determine the existence of tricluster in the Ga-rich region for which R>1.0 in Na2O-Ga2O3-SiO2 system.
Kim, Eun-Yi,Lee, Wan-In,Whang, Chin Myung Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.8
Nanocrystalline $TiO_2$ spherical particle (NP) with a dimension of 5 ${\times}$ 5.5 nm and several nanorods (NR) with different aspect ratios (diameter ${\times}$ length: 5 ${\times}$ 8.5, 4 ${\times}$ 15, 4 ${\times}$ 18 and 3.5 ${\times}$ 22 nm) were selectively synthesized by a solvothermal process combined with non-hydrolytic sol-gel reaction. With varying the molar ratio of TTIP to oleic acid from 1:1 to 1:16, the NRs in the pure anatase phase were elongated to the c-axis direction. The prepared NP and NRs were applied for the formation of nanoporous $TiO_2$ layers in dye-sensitized solar cell (DSSC). Among them, NR2 ($TiO_2$ nanorod with 4 ${\times}$ 15 nm) exhibited the highest cell performance: Its photovoltaic conversion efficiency (${\eta}$) of 6.07%, with $J_{sc}$ of 13.473 mA/$cm^2$, $V_{oc}$ of 0.640 V, and FF of 70.32%, was 1.44 times that of NP with a size of 5 ${\times}$ 5.5 nm. It was observed from the transient photoelectron spectroscopy and the incident photon to current conversion efficiency (IPCE) spectra that the $TiO_2$ films derived from NR2 demonstrate the longest electron diffusion length ($L_e$) and the highest external quantum efficiency (EQE).
Hyorim Choi,Eun Yi Kim,Chin Myung Whang 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.3
New dense composites comprised of a lanthanium manganite system, (La_(1-x)Sr_x)(Mn_(0.85)Fe_(0.0)5Co_(0.05)Ni_(0.05))O_(3+δ)(LSMFCN, Sr^(2+)(x) = 0~0.4 mole) and yttria-stabilized zirconia (YSZ) were fabricated for use as oxygen separation membranes. The densification behavior of the LSMFCN/YSZ composites were studied by sintering with different ratios of LSMFCN and YSZ at various temperatures in air. A density of about 95% was achieved for a sintering temperature of 1200°C. The electrical conductivity of the LSMFCN0/YSZ composites as a function of reciprocal absolute temperature with various YSZ contents was measured. The activation energies for conduction below and above 500°C were about 89 kJ/mol and 68 kJ/mol, respectively. The oxygen permeation flux increased until the YSZ concentration was 60 wt. %, then decreased at 80 wt. % of YSZ. The oxygen permeation flux of the 0.5 mm composite membrane was 1.06 sccm/cm^2 at a 4:6 mixed ratio of LSMFCN0 /YSZ at 1200°C.
졸-겔 공정에 의해 Diol을 기반으로 제조된 PZT막 상전이에 대한 종자 영향
안병헌,황진명,An, Byung-Hun,Whang, Chin-Myung 한국재료학회 1999 한국재료학회지 Vol.9 No.12
diol을 기반으로 하는 Sol-Gel 방법으로 PZT (53/47) 1M sol 용액을 만들어 회전 코팅법으로 Pt/Ti/$SiO_2$/Si 기판위에 코팅하였고 한번 코팅으로 최대 0.9${\mu}m $의 PZT막을 얻었다. PZT는 비강유전성 pyrochlore상을 거쳐 강유전성 perovskite상으로 전이하며 따라서 PZT perovskite seed가 상전이에 미치는 영향을 규명하고자 하였다. 0.2${\mu}m $ 이하의 크기를 갖는 1wt% PZT분말을 propanol용액에 분산시켜 PZT sol 용액에 도입하여 seeded PZT 막을 제조하였다. Seeded PZT막을 열처리한 결과 perovskite상의 생성이 촉진되어 상전이 온도가 50$^{\circ}C$정도 낮아졌다. PZT(53/47) precursor 1M sols were prepared using a diol based Sol-Gel process, and thin films were deposited by spin coating onto Pt/Ti/$SiO_2$/Si substrates. With a single coating, final film thickness of aproximately 0.9${\mu}m $ was achieved from diol-based PZT sol. Since PZT crystallized in a ferroelectric perovskite phase from an intermediate nonferroelectric pyrochlore phase, the effects of the presence of perovskite PZT seeds on the phase transformation of PZT were investigated. Seeded PZT films were prepared from the seeded PZT 1M sols in which seeds with less than 0.2${\mu}m $ in size and 1wt% were dispersed in n-propanol before mixing with the PZT stock solution. The seeding effects were confirmed by the fact that the formation temperature of perovskite phase decreased by 50$^{\circ}C$ with less than 1wt% seeds.